The present invention relates generally to fabrication and curing methods for composite materials, and more particularly to a method for controlling resin cure in the fabrication of composites.
In existing fabrication processes for composite materials, resin cure often requires removal of volatile constituents through partially cured resin as a result of the curing process proceeding generally inwardly of the material. The resultant cured composite structure is therefore frequently characterized by an unacceptably high void volume and degree of microcracking.
The invention has substantially reduced in critical importance previously existing problems with curing processes for composite materials, and finds basis in part in the recognition that the mechanism and rate of removal of volatile constituents from the curing process changes upon gelation of the resin. By maintaining and controlling a preselected temperature differential across the thickness of a composite laminate during the curing process, and allowing one side of the laminate to breathe, a gel front is generated in the laminate which advances with cure of the resin from a heated nonbreathing side of the laminate to the cooled breathing side. Volatile constituents from the curing process are transported toward the breathing side of the laminate ahead of the front through a less viscous, substantially uncured portion of the laminate which facilitates removal of the volatile constituents, avoids stresses internal of the laminate structure which would otherwise result in cracking, and substantially eliminates void formation resulting from trapped residual volatiles. The invention has particular application in fabricating thick or complex composite structures utilizing a condensation curing polymer.
It is therefore a principal object of the invention to provide an improved composite fabrication method.
It is another object of the invention to provide a method for controlling resin cure in the fabrication of composite materials.
These and other objects of the invention will become apparent as the detailed description of representative embodiments proceeds.